5b4c5 x 6b3c2 =
$$\begin{array}{rcl}\mathbf{5b^4c^5 \cdot 6b^3c^2 }\\&=& 5\cdot 6 b^4b^3c^5c^2\\&=& 30 \cdot b^{4+3}\cdot c^{5+2}\\\mathbf{5b^4c^5 \cdot 6b^3c^2 }& \mathbf{=} & \mathbf{30 b^7c^7}\\\hline\\\end{array}$$
